If profit is 20% of the selling price, then profit is what percent of the cost price?

let the SP(selling price) of the item be Rs 100

profit is 20% of SP , so $$\frac{20}{100}\times SP$$ here SP=100 

profit = $$\frac{20}{100}\times100$$ = 20 therefore we get Rs 20 as profit

Now we know SP = CP + Profit , substituting the values of SP and Profit we get CP(cost price)

CP = SP - profit

CP = 100 - 20 = 80

profit as a percent of CP is $$\frac{profit}{CP}\times 100$$

$$\frac{20}{80}\times 100$$= 25%